This invention relates to a process for making substituted biphenols. In particular, this invention relates to a process for making substituted biphenols by reacting phenols with diphenoquinones.
Biphenols are useful as bactericides, chemical intermediates, copolymers, and especially as antioxidants. For example, 2,2',6,6'-tetra-t-butyl-p,p'-biphenol is an excellent antioxidant in a broad range of organic materials. It can be used to stabilize such materials as animal and vegetable fats or oils, gasoline, lubricants, polyolefins such as polyethylene and polypropylene, and both natural and synthetic rubber. It exerts its protective effect by merely incorporating it uniformly throughout the organic material in small amounts. Concentrations of from about 0.1 to 1 weight percent usually provide adequate antioxidant protection. When the substituted p,p'-biphenol compound contains easily removable alkyl substituents such as tertiary alkyl, the compound may also be easily dealkylated to form p,p'-biphenol, a useful monomer in polyester production.
In U.S. Pat. No. 3,562,338, a process for preparing these compounds is disclosed in which 3,3',5,5'-tetrahydrocarbyl diphenoquinones are first prepared by an oxidative coupling reaction of a 2,6-dihydrocarbyl phenol in the presence of an alkali metal hydroxide. The 3,3',5,5'-tetrahydrocarbyl diphenoquinone is then allowed to react with extra 2,6-dihydrocarbyl phenol to form the desired product 2,2',6,6'-tetrahydrocarbyl-p,p'-biphenol.
Similarly, in U.S. Pat. No. 3,631,208 substituted biphenols were prepared by reaction of phenols with diphenoquinones in the presence of acidic or basic catalysts such as carboxylic acids, amines or metal hydrocarbon oxides.
Because prior art processes employed acidic or basic catalysts a separate neutralization step was required to neutralize the catalyst which results in contamination of products with salt by-products.